In recent years, electronic products have had smaller size and lighter weight. With such a trend, semiconductor devices have also become increasingly smaller with more enhanced functionalities, thereby making it necessary to develop various semiconductor packaging technologies. Among them, so-called TSV (Through Silicon Via) package is drawing attentions due to its high performance but micromini size. In such a TSV packaging process, after TSV is formed through a bond pad region of a silicon die, it is filled with metal so as to form a through electrode.
It is now explained in more detail about the TSV packing process. The process includes the steps of: forming a via hole in a silicon wafer; forming an isolation layer and a diffusion barrier layer in that order on an inner side of the via hole; filling the via hole with metal; thinning the silicon wafer; and forming and bonding a bump. Among those steps, the via filling step occupies about more than 40% of the total process cost. Accordingly, it is urgent and important to have a low cost via filling step in order to commercialize the TSV packaging process.
It is a CU electroplating technology that is more used than the other prior art via filling technologies. The CU electroplating technology has been widely used after the development of a CU damascene process, but yet there are many problems in applying it to the via filling step of the TSV packaging process.
In detail, since the via hole of the TSV package is much bigger than what can be formed by the damascene process in its diameter of about 1 to 200 micrometers and in its depth of about 10 to 300 micrometers, it takes too much time to fill the via hole by using the CU electroplating technology, and additives and process conditions should be very carefully controlled to prevent void problem inside the via hole or an overburden problem at a top portion of via hole.
Recently, a dry filling method is suggested as an alternative to the CU electroplating technology that would result in such a long processing time. In the dry filling method, after a via hole is formed in a substrate, those steps of printing a metal paste, decompression, and compression are repeated by using a VPES (Vacuum Printing Encapsulation System) so as to fill the via hole with the metal paste, which is then cured to finally form a metal electrode. Such a dry filling method, however, needs a very expensive equipment that is capable of decompressing and compressing as well as printing the metal paste in a vacuum condition. Further, it is difficult to fabricate a dense electrode because voids may be relatively easily formed in an organic material portion of the metal paste during the step of curing. Another problem is that a residue of the metal paste cannot be easily removed from a wafer.